Magnetic and Crystalline Microstructures of Fe–Pt–B Nanocomposite Ribbons

We investigate magnetic and crystalline microstructures of melt-spun (Fe0.675Pt0.325)(100-x)B-x (x = 12, 14, 16, 18, 20) nanocomposite ribbons after optimal thermal treatment using a magnetic force microscope. The magnetic microstructures are characterized by darker spots adjacent to brighter ones in a sub-micro scale and in random distribution. It is found that the strength of the exchange coupling interaction between the crystals in the 10-100nm scale, implied by the maximum value (delta M)(max) of the Henkel plot, could be roughly described by the ratio of the average width of the magnetic spots (w) over bar to the average crystal size (D) over bar for the ribbons. Moreover, we find that the intrinsic coercivity H-j(c) of the ribbons is sensitive to their crystal sizes, and the smaller (D) over bar, the higher jHc. Finally, by using roughness analysis, the curve of the root mean square values of the phase shift of the magnetic force images versus the boron content x is obtained, which is qualitatively consistent with that of the magnetization sigma(12)kOe of the ribbons versus x.